CGS Slope Detectors

slope_detectors_panelQuantity: 2 in one 1U panel
Ken Stone’s CGS 62 Slope Detector:

The slope detector is an event-driven gate/trigger generating device. It monitors a control voltage, and responds according to what that voltage is doing. If the voltage is rising, the slope detector gives a “gate” output (approx. 5V) on its “rising” output. Likewise, if the voltage is falling, the slope detector gives an output on its “falling” output. The duration of this gate signal depends on the incoming CV and the setting of the sensitivity pot. When the CV is remaining constant, the “steady” output activates.

These gate signals can be used to fire envelope generators dependent on the action of the CV, for example opening a filter when a melody is rising in pitch, and closing it when the melody is falling in pitch. It can also be used to generate gate signals from LFOs, envelope generators, to advance sequencers etc.

The sensitivity pot allows the slope detector to work with either relatively fast events, like the edges of a square wave pulse train, or very slow events, such as the sine output of an LFO being used to drive filter/phaser sweeps.

This is a dual module, housed in a Front Panel Express Panel of my own design. It’s the first of four modules planned in this style, which has sixteen equally spaced positions (8 x 2) where pots, jacks, switches, or LEDs can be placed. The vertical spacing between components is one inch and the horizontal 0.85 inches, which is the same as MOTM jack spacing. The use of 16mm Alpha pots and 3/4-inch Alco knobs allows the placement of pots anywhere. This is the design insight and also the main compromise. The Slope Detector has one pot, three LEDs and four jacks, perfectly fitting two of them into a 1U panel.  The red LED comes in a chrome bezel, Lumex PN: SSI-LXR4815ID.  SSI-LXR4815YD and SSI-LXR4815GD are yellow and green. I use green to indicate positive voltages, so I chose it to indicate Rising.

Modifications:  I changed the voltage divider resistors on the outputs to be 3K3/1K8 instead of the original 1K8/1K to reduce current draw.  I use these values for all of my digital outputs.  RLED is 2K2 ohms.

The 3-jack bracket from Bridechamber allows mounting the PC boards adjacent to each other.  (Two additional holes need to be drilled.)

slope_detectors_back

Here it is in the cabinet, next to a standard MOTM format module. The most unusual thing is the LEDs located in what’s normally the jack region. I think the smaller knob fits in well.

slope_detectors_in_cabinet

2 Responses to CGS Slope Detectors

  1. tim says:

    Hi, how does the slope detector detect the rising or falling slope? I’d imagine there is some kind of comparator at work? Thanks as always for keeping up with this site!

  2. Richard says:

    Hi Tim. If you look at the schematic diagram, linked at the top of this page, you’ll see how two comparators are used to compare the existing voltage with the new voltage delayed by a capacitor.

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